Process for obtaining modified polyethylene terephthalate pilling-free fibres originating from the polymer thus modified

ABSTRACT

The present invention relates to a process for obtaining continuously polyethylene terephthalate modified by --SiO-- groups in a proportion of 30014 700 ppm of Si during the direct esterification reaction between terephthalic acid and ethylene glycol, followed by polycondensation in a known manner by introducing methoxyethyl silicate or propyl silicate at a time when the prepolymer has a weight-average molecular mass of between 9,000 and 16,000, a polydispersity index of between 1.5 and 2, and when it is at a temperature of between 260° and 290° C., and at a pressure of between 1.5 and 2.5 bars, the silicate/prepolymer reaction time being at least 5 minutes. 
     The present invention also relates to pilling-free fibers originating from the modified polyethylene terephthalate and to a process for obtaining them.

This is a division of application Ser. No. 07/678,844 filed Apr. 3,1991, now U.S. Pat. No. 5,300,626.

The present invention relates to a process for obtaining polyethyleneterephthalate containing --SiO-- groups by direct esterification ofterephthalic acid (TA) and of ethylene glycol (EG) and to thepolyethylene terephthalate thus obtained.

It also relates to the pilling-free fibres with improved characteristicsoriginating from this polymer and a process for obtaining them.

Fibres based on polyethylene terephthalate (PET) are well known fortheir properties and their ease in maintenance and use.

However, their use for obtaining textile articles is limited by the"pilling" phenomenon. "Pills" or "pilling" means the formation of smallmodules on the surface of the textile articles produced. This resultsfrom the fact that the ends of fibres projecting from the surface orfree ends of the fibres form balls and, because of the good toughness ofthe fibres, do not fail but remain adhering to the surface. Mechanicalremoval of the nodules, such as brushing and shaving is very tedious andcostly and, what is more, produces only a poor result because new"pills" are continually being formed.

Many attempts have been made to overcome this disadvantage.

One of the most widespread means for obtaining pilling-free staplefibres consists of embrittling the fibres. This can be done, forexample, by creating microscopic irregularities in the fibre, but themost commonly used method is certainly the reduction in the end-to-endlength of the macromolecular chains. However, this produces a decreasein the melt viscosity of the polymer, resulting in problems in spinning,which it has been attempted to solve in various ways. Embrittlement ofthe fibres also produces a degradation in the processability of thefibres obtained during the spinning and weaving operations.

One of the best known and most widely employed methods consists,according to French Patent No. 1,603,030 to Rhodiaceta, in introducingtri- or tetrafunctional products in the macromolcular chains, enablingthe end-to-end length of the macromolecular chains to be reduced whilemaintaining a high melt viscosity. This reduction increases with theproportion of branching agent and its functionality. This solutiongenerally gives a correct antipilling property which is maintained afterthe articles are dyed. However, for processability with cotton fibres,fibres of polyethylene terephthalate (PET) modified with branchingagents have an elongation which is too high and tenacities which are toolow for use in weaving fibre spun yarns.

Another route which is already employed consists in introducing into themacromolecular chains weak chemical bonds which degrade duringsubsequent treatment in the presence of water or steam.

For example, French Patent No. 2,290,511 proposes to introduce 0.01 to2% by weight of diphenylsilanediol relative to dimethyl terephthalate(DMT) before the tranesterification. However, the elongations at breakare too high to permit processability with cotton fibres and thetenacities are too low for running the fibre spun yarns on looms.

French Patent No. 1,589,057 proposes to introduce into thepolycondensation a compound of formula: ##STR1## capable of improvingthe pilling of the fibres and U.S. Pat. No. 3,335,211 describesobtaining fibres exhibiting improved pilling from an anhydrous PET ofmelt viscosity (MV) of 1,000-6,000 poises (measured at 275° C.),containing 0.1-0.75 gram-atoms of Si per 100 moles of glycol, byintroducing into the polycondensation a compound of formula: ##STR2##where R, R', R" are carbon or oxyhydrocarbon radicals containing 1 to 6carbon atoms, Z is a saturated divalent hydrocarbon group consisting 1to 6 carbon atoms, x=1-20 and n=0-2.

However, after wet treatment, such fibres have elongations which are toolong to permit processability as a mixture with cotton fibres and/ortenacities which are too low at the fibre spun yarn stage for spun yarnsto be employed in weaving.

Modified polyethylene terephthalate fibres have now been found whichhave, at the same time, a low elongation close to that of cotton,permitting the fibres to be processed by themselves or mixed with cottonfibres, a high tenacity making it possible to obtain fibre spun yarnswhich are suitable for the weaving operation and which exhibit goodantipilling properties, these being prepared from a modifiedpolyethylene terephthalate (PET), originating directly from terephthalicacid (TA) and ethylene glycol (EG).

More particularly, the present invention relates to a continuous processfor direct esterification between TA and EG, followed bypolycondensation in a known manner to obtain PET modified by thecontinuous introduction of methoyethyl silicate or propyl silicate in aproportion of 300 to 700 ppm or 400 to 600 ppm by weight of silicon at atime when the prepolymer has a weight-average molecular mass Mw ofbetween 9,000 and 16,000, a polydispersity index I=Mw/Mn of between 1.5and 2, and when it is at a temperature of between 260° and 290° C., at apressure of between 1.5 and 2.5 bars, the silicate/prepolymer reactiontime being at least 5 min, preferably at least 7 min.

The present invention also relates to a PET modified with --SiO-- groupswhich are chemically bonded to the macromolecular chains and present ina proportion of 300-700 ppm by weight of silicon, free from esterinterchange catalyst residues, and to pilling-free fibres capable ofbeing employed as a mixture with cotton fibres for weaving, additionallyhaving an elongation at break ≦25%, preferably ≦20%, a tenacity at break≧40 cN/tex, preferably ≧45 cN/tex, a boiling water shrinkage of between1.5 and 6% and a post-dyeing flex abrasion index (FAI) ≦6,500.

The present invention relates to a process for obtaining modified,pilling-free PET fibres with a melt viscosity of between 600 and 1,000poises (measured at 290° C. and at a shear rate lower than 100 s⁻¹), bymelt spinning in a known manner, a first drawing in an aqueous bathmaintained at a temperature of between 40° and 70° C. to a ratio ofbetween 2.9 and 4.6 x, a second drawing in the presence of steam at atemperature of between 100° and 110° C. to a ratio of 1.05-1.2 x,setting at a temperature of between 160° and 200° C., preferably170°-180° C. at a tension such that the filaments retract to a ratio of0.95-1 x followed by sizing, drying, crimping and cutting to a length of3-5 cm.

The modified PET originates from the continuous reaction of directesterification between TA and excess EG in a known manner, at atemperature of between 270° and 300° C. and under pressure, optionallyin the presence of a direct esterification catalyst such astriethanolamine orthotitante, followed by continuous polycondensation inthe presence of known catalysts such as antimony oxide, under vacuum, ata temperature of between 270° and 300° C.; the introduction ofmethoxyethyl or propyl silicate is performed at the time when the weightmolecular mass of the prepolymer is between 9,000 and 16,000, preferablybetween 11,000 and 14,000, the polydispersity index Mw/Mn is between 1.5and 2, preferably 1.7 to 1.9 and where the temperature of the reactionmixture is between 260° and 290° C. and the pressure is between 1.5 and2.5 bars.

The direct esterification reaction between TA and EG is performed withthe removal of water throughout the esterification and polycondensationreactions and it is quite surprising that it is possible to obtain a PETcontaining 300 to 700 ppm, preferably 400 to 600 ppm, of silicon in theform of --SiO-- units fixed in the macromolecular chains withoutproducing the hydrolysis phenomenon which must be absolutely avoidedbefore the spinning, as follows from U.S. Pat. No. 3,335,211, col. 3,lines 50-70.

Still according to this Patent, it is clear that this phenomenon is easyto avoid when the PET is obtained by ester tranesterification, that isto say from dimethyl terephthalate (DMT) and EG, since this reaction isperformed only with the release of methanol; in contrast, it is quiteastonishing that the modified PET can be obtained without beinghydrolysed, using a direct esterification and polycondensation processproducing water, a process which, furthermore, has better kinetics,presents fewer risks of polymer degradation and is consequently aprocess which is more preferable because of being more industrial andeconomical.

It is essential, furthermore, that the addition of methoxyethyl orpropyl silicate should be performed while the polyester has aweight-average molecular mass Mw of between 9,000 and 16,000, preferably11,000 to 14,000. If the addition is made when the Mw is too low, thewater present during the continuous polymerisation converts the silicateinto silica and alcohol and therefore prevents the formation of the--SiO-- groups in the macromolecular chains and prevents thepolycondensation reaction by blocking the acidic chain ends, because thealcohol released is monofunctional. If, on the contrary, the Mw is toohigh the silicate does not have time to react with the polyester beingformed, since a continuous process is taking place.

Similarly if the temperature of the reaction mixture is too low, thereaction does not take place; if the temperature is too high than apolymer degradation is observed.

Equally, the proportion of silicate which is introduced is critical;

below 300 ppm of silicon the antipilling effect of the finished fibresand subsequently of the woven or knitted articles is insufficient,

above 700 ppm of silicon the continuous esterification andpolycondensation reaction reverses and it is impossible to obtain aspinnable PET.

The modified PET thus obtained contains:

--SiO-- groups chemically bonded to the polymer in a proportion of 300to 700 ppm of silicon calculated relative to the polyester, preferably400 to 600 ppm of Si,

and is free from catalyst residues which are specific to theterephthalic ester interchange reactions.

In addition, it has a COOH end group content ≦20 g/t, preferably ≦12 g/tand a melt viscosity which is generally between 600 and 1,000 poises at290° C., preferably between 700 and 900 poises, measured at a shear rate≦100 m⁻¹.

After the polycondensation the modified polyester of weight-averagemolecular mass of between 25,000 and 35,000 is spun continuously througha fibre-type die comprising a large number of holes (for example800-1,500) in which the flow rate varies as a function of the desiredcount. The filaments, taken up at a speed which is generally between 800and 1,500 m/min, are then drawn firstly in an aqueous bath maintained at40°-70° C., preferably 50°-60° C., to a ratio of 2.9-4.6 x, preferablybetween 3.5-4.5 x, then again in the presence of steam at 100°-110° C.,to a ratio of 1.05-1.2 x, by means of any known device, so as to obtainan overall ratio of between 3.5 and 4.8 x, preferably between 4 and 4.8. The filaments are then set under a tension such that they undergo aslight retraction of 0.95 to 1 x, and are then sized and dried on a beltat approximately 100° C. and are then crimped and cut to a length of 3-5cm.

The yarns thus obtained have:

an elongation ≦25%, preferably ≦20%

a shrinkage of between 1.5 and 6%, preferably 4 to 6%

a tenacity at break ≧40 cN/tex, preferably ≧45 cN/tex

and, after dyeing:

a flex abrasion index (FAI) ≦6,500, preferably ≦6,000.

The FAI enables the antipilling property to be assessed on the fibres.

FAI means the measurement of the flex abrasion resistance, whichconsists in determining the breaking strength of fibres which are keptstretched over a steel wire whose diameter is a function of the fibrecount at a folding angle of 110° and driven in a to-and-fro motion in aconditioned atmosphere (T=22° C. ±2° C.--RH: 65% ±2%); the flex abrasionindex, FAI, is equal to the number of cycles before breaking. The FAIvalues are related to the filament count of the fibres and areproportionately higher the lower the count.

The fibres for cotton generally have a count ≦2 dtex/filament. Thefibres obtained have an elongation which approaches that of cotton, thusallowing good processability with cotton fibres, a high tenacityenabling them to be run on looms without risks or breaking of fibre spunyarns and a sufficiently low pilling after dyeing on the articles thusobtained, on wovens in particular. They make it possible to avoidsubsequent finishing treatments such as singeing or brushing/shaving,which are industrially demanding and costly and are necessarily employedon woven fabrics obtained from conventional fibres. The fibres thusobtained are easily convertible into fibre spun yarns by conventionalring or open-end spinning techniques, either by themselves or mixed withcotton spun yarns, using a process which is simple and inexpensive onindustrial scale.

In the examples which follow, the mechanical characteristics aredetermined by conventional tensile measurements on a manual or automatictensometer, at a constant shear rate on a fibre specimen subjected tolengthwise pull until it breaks; since the tensometer is connected to acomputer, the following numerical values are supplied, which correspondto a mean of 30 measurements:

initial count in dtex

the force at break

the tenacity A

the elongation at break ##EQU1##

The measurement of the shrinkage of a yarn consists in determining thechange in length of a yarn specimen under standard pretension (50mg/dtex) after a heat treatment. In the case of the determination ofboiling water shrinkage, the heat treatment is as follows:

15 min in boiling water

10 min in an oven at 80° C.

1 h in a conditioned atmosphere

Calculation of the shrinkage: ##EQU2##

The warp and weft fabrics prepared according to the invention retaingood antipilling properties evaluated according to the R.T.P.T. test andgood tensile measurements on spun yarns and on fabric in respect of thetenacity breaking and elongation when compared with commercially knownspun yarns and fabrics.

The R.T.P.T. test applies to woven fabrics (or knits) based on fibresaccording to the method described in the AFNOR standard G 07-121. It iscarried out as follows:

three 100-cm² circular specimens whose periphery is hardened by adeposit of neoprene-based adhesive are subjected for a given time tostirring in a R.T.P.T. chamber whose interior is lined with a neoprenetape. The pilling of the specimens is graded visually by comparison withphotographic standards (1: very many pills→5: no pill).

Tensometric Measurements on Spun Yarns

These are carried out by means of an Uster trademark automatictensometer on 50-cm specimens under a pretension of 400 g. Thetensometer is adjusted beforehand to a breaking time of 20 seconds. Theinstrument gives 1 measurement of elongation at break. ##EQU3##

Total strength=breaking load in g.

The values correspond to averages over 120 measurement.

Transometric Measurements on Fabrics

The tests are performed in the weft and warp directions.

A frayed fabric speciment 5 cm in width is subjected to a lengthwisepull until it breaks.

The force in daN and the elongation in % at the break point arerecorded.

Measurement of The Number of End Groups

The measurement of the number of end groups of the modified PETaccording to the invention is performed as follows:

exactly approximately 3 g of granular polymer are dissolved in 50 ml ofortho-cresol at 90° C. and an acidimetric determination is performedusing 0.02N aqueous sodium hydroxide.

EXAMPLE 1

A modified PET is prepared continuously by direct esterification andpolycondensation of TA and EG with a TA/EG molar ratio=1.15 under thefollowing conditions:

1) slurrying TA with ethylene glycol in a first stirred reactor in thepresence of triethanolamine orthotitanate known in the trade under thetrademark Natol S in a proportion of 4 ppm of Ti,

2) the slurried mixture is then heated in a second reactor to 275° C. ata pressure of 6.6 bars with the removal of water,

3) the prepolymer is then heated to 278° C. at 1 bar in a third reactor,

4) the product then moves to a fourth reactor in the presence of aglycolic solution of Sb oxide at a rate of 17.4 l/hour (200 ppm Sb) and5.9 kg/hour of TiO₂ in suspension in 19 l/hour of EG, where the productis heated to 282° C. at a pressure of 35 torr,

5) then, at the outlet of the fourth reactor, methoxyethyl silicate isintroduced continuously at a rate of 8.3 l/hour (that is 500 ppm of Si),while the PET has a weight molecular mass of 11,570, a polydispersityindex of 1.51 and while the pressure is approximately 2 bars and thetemperature 280° C.,

6) the mixture is then introduced into a last stirred reactor, heated to283° C. at a pressure of 2 torr, to complete the polycondensation. Thereaction time between the silicate and the prepolymer is approximately 6minutes.

The modified PET with a melt viscosity of 1,000 poises, maintained at280° C. is conveyed directly to a spinning frame comprising 30 dies of156-mm diameter, pierced with 1226 holes of 0.28-mm diameter, at a flowrate of 790 g/min per die. The filaments are cooled by two miniblowerssituated on either side of the die and offset relative to each other;the air is blown transversely in relation to the bundle of filaments ata temperature of 23° C. The filaments are then collected to form asliver; the 30 slivers are sized individually and are then assembled andrun over 6 rollers controlling the speed and then between 2 crenellatedrollers at a speed of 1,100 m/min and are recovered in a spinning can.

40 slivers such as obtained above are assembled and the rope is thensized and then drawn firstly in an aqueous bath 4 m in length andmaintained at approximately 50° C. to a draw ratio of 3.6 x and thensecondly in a tube 8 m in length containing steam at 110° C., to a ratioof 1.14 x. The overall ratio is 4.10 x.

The rope of filaments is then set under tension with a retraction ratioof 0.98 x on 12 rollers heated to 175° C. at a speed of 200 m/min, issized, crimped in a crimping box and is then dried at 100° C. byhigh-frequency heating.

The rope is cut into the form of fibres of a mean length of 35-45 mm.

The characteristics of the fibres obtained are as follows:

    ______________________________________                                        Count dtex/filament    1.61                                                   Tenacity in cn/tex     44.1                                                   Elongation in %        24.8                                                   Shrinkage in %         4.7                                                    FAI: before dyeing     5,700                                                  after dyeing           4,800                                                  ______________________________________                                    

Dyeing is carried out at a temperature of 130° C. for 30 min and underpressure.

Using the fibres obtained above, fibre spun yarns are prepared as a50/50 (50 m in 1 g) by an open-end process with a rotor speed of 65,000rev/min.

The fibre spun yarn obtained, intended for weaving, has the followingcharacteristics:

    ______________________________________                                        Twist turns/meter       919 Z direction                                       Elongation at break %   8.9                                                   Metric count (Nm)       48.9                                                  Total strength at break (g)                                                                           260                                                   ______________________________________                                    

Using the above fibre spun yarns a fabric is produced, in which both thewarp and the weft consist of the above 50/50 fibre spun yarns on arapier loom (Saurer 400 trademark) under the following conditions:

cloth weave

warp sized in the usual manner

textile structure:

warp 30 yarns/cm

weft 27 strokes/cm

weight per m², 118 g

The fabric was dyed at 125° C. in the case of the polyester and 80° C.in the case of the cotton after heat treatment at 180° C.

The fabric thus obtained has the following tensile measurements onfabric:

    ______________________________________                                        Break strength (kg)    Break elongation %                                     warp     weft          warp     weft                                          ______________________________________                                        46.5     41.4          14.2     20.1                                          ______________________________________                                    

R.T.P.T. pilling test on fabric (AFNOR standard G-07-121)

    ______________________________________                                        5'         15'   30'          45' 55'                                         ______________________________________                                        4          3     3            3   4                                           ______________________________________                                    

When a fabric is subjected to a brushing/shaving treatment usuallyemployed to improve the pilling characteristics of the fabrics, theR.T.P.T. test gives the following results:

    ______________________________________                                        5'         15'   30'          45' 55'                                         ______________________________________                                        4          4     4            4   4                                           ______________________________________                                    

Such a brushing/shaving treatment, which is costly on industrial scale,becomes superfluous.

EXAMPLE 2 Comparative

Example 1 is reproduced, except for the steam setting treatment, whichis carried out at 140° C. without tension.

The characteristics of the yarns obtained are as follows:

    ______________________________________                                        Count dtex/filament     1.80                                                  Tenacity in cN/tex      33.3                                                  Elongation in %         65                                                    Shrinkage in %          3.6                                                   FAI: before dyeing      5,900                                                 after dyeing            5,050                                                 ______________________________________                                    

The fibres obtained are converted into fibre spun yarns mixed 50/50 withcarded cotton fibres, of metric count 48.9 using the open-end process.

The fibre spun yarns obtained exhibit the following characteristics:

    ______________________________________                                        Nm                      48.9                                                  Elongation at break %   7.9                                                   Total strength (g)      225                                                   ______________________________________                                    

The fibre spun yarns exhibit poor characteristics, in particularstrength, which are due to the inadequate characteristics of the fibresthemselves.

They were converted into fabrics with mediocre performance on fabricsand a poor yield, making such fibres and spun yarns of no interest in anindustrial application.

    ______________________________________                                        Break strength (kg)    Break elongation %                                     warp     weft          warp     weft                                          ______________________________________                                        39.2     33.3          11.9     19.5                                          ______________________________________                                    

EXAMPLE 3 Comparative

Example 1 is reproduced without introducing silicate and with operationat higher polycondensation temperatures of the order of 290° C. The PEThas a melt viscosity of approximately 2,000 poises.

The process for obtaining the yarns is identical except for the take-upspeed: 1,650 m/min, the drawing in an aqueous bath to a ratio of 2.59and the heat setting temperature of 185° C.

    ______________________________________                                        Count dtex/filament      1.57                                                 Tenacity in cN/tex       57.2                                                 Elongation in %          23                                                   Shrinkage in %           4.2                                                  FAI: before and after dyeing                                                                           35,000                                               ______________________________________                                    

It was possible to obtain fibre spun yarns without any problem by theprocess described in Example 1, as a 50/50 mixture with cotton fibres.

    ______________________________________                                        Metric count (Mm)       48.9                                                  Elongation at break %   9.4                                                   Total strength (g)      303                                                   ______________________________________                                    

A fabric was also obtained as shown in Example 1.

    ______________________________________                                        Break strength (kg)    Break elongation %                                     warp     weft          warp     weft                                          ______________________________________                                        39.2     35.3          11.9     19.5                                          ______________________________________                                    

R.T.P.T. test on fabric (AFNOR standard G-07-121)

    ______________________________________                                                        5'   15'   30'     45' 55'                                    ______________________________________                                        without brushing/shaving                                                                        3/4    2     1     1   1                                    with brushing/shaving                                                                           4      3     2     2   2                                    ______________________________________                                    

The FAI tests on the fibres are very poor and although fabrics with goodstrength have been obtained, the pilling tests on fabrics even with abrushing/shaving treatment remain quite inadequate.

EXAMPLE 4 Comparative, TMP

Example 1 is reproduced, methoxyethyl silicate being replaced withtrimethylolpropane (TMP) introduced between the 3rd and 4th reactor in aproportion of 0.6 mol % relative to terephthalic acid (according to FR1,603,030).

The PET obtained, of same melt viscosity as according to Example 1, isobtained as shown in Example 1, except for the following parameters:

    ______________________________________                                        die flow rate                                                                             650 g/min                                                         bath drawing                                                                              ratio: 2.7 × temperature: 50° C.                     steam drawing                                                                             ratio: 1.1 × temperature: 110° C.                    setting under tension                                                                     total ratio: 2.97 × temperature: 170° C.             ______________________________________                                    

The draw ratio is a limiting ratio, filament breakage takes place aboveit.

    ______________________________________                                        Mechanical characteristics:                                                   ______________________________________                                        Count dtex/filament      1.62                                                 Tenacity in cN/tex       33.5                                                 Elongation in %          32.8                                                 Shrinkage in %           3.6                                                  FAI before and after dyeing                                                                            5,000                                                ______________________________________                                    

The tenacity and elongation characteristics, outside the invention, didnot make it possible to obtain fibre spun yarns, by themselves or mixedwith cotton fibres, by the open-end process under industrial conditions.

EXAMPLE 5

Example 1 is reproduced in respect of obtaining polyethyleneterephthalate by using 600 ppm of Si in the form of methoxyethylsilicate introduced continuously at a rate of 10.2 l/hour. Spinning anddrawing are performed as in Example 1 to a ratio of 3.33 in an aqueousbath maintained at 65° C. and then in the presence of steam to a ratioof 1.23, the overall ratio being 4.1 x. The rope of filaments is thenset under tension with a retraction ratio of 0.98 x on 12 rollers heatedto 170° C., and is sized, crimped and dried under the conditionsdescribed in Example 1.

The rope is cut into the form of fibres with a mean length of 35-45 mm.The characteristics of the fibres are as follows:

    ______________________________________                                        Count dtex/filament     1.52                                                  Tenacity in cN/tex      40                                                    Elongation in %         19.8                                                  Shrinkage in %          4.2                                                   FAI before dying        5,400                                                 FAI after dyeing        4,400                                                 ______________________________________                                    

Dyeing was performed as in Example 1.

Using the fibres obtained above, fibre spun yarns are prepared as a50/50 mixture with carded cotton fibres, by an open-end process, onewith a rotor speed of 72,000 rev/min (5A), the other with a rotor speedof 92,000 rev/min (5E).

The fibre spun yarns obtained, intended for weaving, have the followingcharacteristics:

    ______________________________________                                        Metric count       50.4       50.2                                            Strength g         260        236                                             Elongation at break %                                                                            7.6        6.4                                             Twist turns/min    919 Z      919 Z                                           ______________________________________                                    

Using the above fibre spun yarns, two fabrics A and B are produced, inwhich the warp and the weft consist of the above 50/50 fibre spun yarns.

The fabrics are produced on a rapier loom (Saurer trademark) under thefollowing conditions:

cloth weave

warp sized in the usual manner

fabric structure:

warp 30 yarns/cm

weft 26 strokes/cm

weight per m² : 115 g

The fabric was dyed at 125° C. in the case of the polyester and 80° C.in the case of the cotton after heat treatment at 180° C.

R.T.P.T. test on fabric (AFNOR standard G-07-121)

    ______________________________________                                        5'           15'    30'        45'  55'                                       ______________________________________                                        A     4/5        1      3/4      4    4/5                                     B     4          3      4        4    5                                       ______________________________________                                    

It is interesting to find that the fibre spun yarns according to theinvention withstand high speeds by the open-end process, whichrepresents a major economic industrial advantage. Moreover, the abovepilling tests show that the brushing/shaving treatment is unnecessary onthe fabrics produced from the fibres according to the invention.

EXAMPLE 6

A modified PET is prepared continuously by direct esterification andpolycondensation of TA and EG with a TA/EG molar ratio=1.15 under thefollowing conditions:

1) slurrying of TA with ethylene glycol in a first stirred reactor inthe presence of triethanolamine orthotitanate known in the trade underthe trademark Natol S in a proportion of 4 ppm of Ti,

2) the slurried mixture is then heated in a second reactor to 275° C. ata pressure of 6.6 bars with the removal of water,

3) the prepolymer is then heated to 278° C. at 1 bar in a third reactor,

4) the product then moves to a fourth reactor in the presence of aglycolic solution of Sb oxide at a rate of 17.4 l/hour 200 ppm Sb) and5.9 kg/hour of TiO₂₂ in suspension in 19 l/hour of EG, where the productis heated to 282° C. at a pressure of 35 torr,

5) then, at the outlet of the fourth reactor, propyl silicate isintroduced continuously at a rate of 7.3 kg/hour (that is 545 ppm ofSi), while the PET has a weight molecular mass of 11,570, apolydispersity index of 1.51 and while the pressure is approximately 2bars and the temperature 280° C.,

6) the mixture is then introduced into a last stirred reactor, heated to283° C. at a pressure of 2 torr, to complete the polycondensation.

The reaction time between the silicate and the prepolymer isapproximately 6 minutes.

The modified PET with a melt viscosity of 850 poises, maintained at 280°C. is conveyed directly to a spinning frame comprising 30 dies, of156-mm diameter, pierced by 1226 holes 0.28 mm in diameter, at a flowrate of 790 g/min per die. The filaments are cooled by two miniblowerssituated on either side of the die and offset relative to each other;air is blown transversely in relation to the bundle of filaments at atemperature of 23° C. The filaments are then collected to form a sliver;the 30 slivers are sized individually and are then collected and runover 6 rollers controlling the speed and then between 2 crenellatedrollers at a speed of 1,100 m/min and are recovered in a spinning can.

40 slivers such as obtained above are assembled and the rope is sizedand then drawn firstly in an aqueous bath 4 m in length maintained atapproximately 50° C. to a draw ratio of 3.29 x and then secondly in atube 8 m in length containing steam at 110° C. to a ratio of 1.23 x. Theoverall ratio is 4.05 x.

The rope of filaments is then set under tension with a retraction ratioof 0.98 x on 12 rollers heated to 175° C. at a speed of 200 m/min and issized, crimped in a crimping box and then dried at 100° C. usinghigh-frequency heating.

The rope is cut into the form of fibres with a mean length of 35-45 mm.

The characteristics of the fibres obtained are as follows:

    ______________________________________                                        Count dtex/filament    1.56                                                   Tenacity in cN/tex     41                                                     Elongation in %        22                                                     Shrinkage in %         4.1                                                    FAI: before dying      7,000                                                  after dying            4,800                                                  ______________________________________                                    

Dyeing is performed at a temperature of 130° C. for 30 min and underpressure.

Using the fibres obtained above, fibre spun yarns are prepared as a50/50 mixture with carded cotton fibres of metric count 50/1 (50 m in 1g) by an open-end process with a rotor speed of 65,000 rev/min. Thefibre spun yarn obtained, intended for weaving, has the followingcharacteristics:

    ______________________________________                                        Twist turns/meter     919 Z direction                                         Elongation at break % 8.5                                                     Metric count (Nm)     49                                                      Total strength at break (g)                                                                         245                                                     ______________________________________                                    

Using the above fibre spun yarns, a fabric is produced in which both thewarp and the weft consist of the above 50/50 fibre spun yarns, on arapier loom (Saurer 400 trademark) under the following conditions:

cloth weave

warp sized in the usual manner

fabric structure:

warp 30 yarns/cm

weft 27 strokes/cm

weight per m² : 118 g

The fabric was dyed at 125° C. in the case of the polyester and 80° C.in the case of the cotton after heat treatment at 180° C.

The fabric thus obtained has the following tensile measurements onfabric:

    ______________________________________                                        Break strength (kg)    Break elongation %                                     warp     weft          warp     weft                                          ______________________________________                                        45       40.9          14.2     20.1                                          ______________________________________                                    

R.T.P.T. pilling test on fabric (AFNOR standard G-07-121)

    ______________________________________                                        5'         15'   30'          45' 55'                                         ______________________________________                                        4          3     3            3   4                                           ______________________________________                                    

When a fabric is subjected to a brushing/shaving treatment usuallyemployed to improve the pilling characteristics of the fabrics, theR.T.P.T. test gives the following results:

    ______________________________________                                        5'         15'   30'          45' 55'                                         ______________________________________                                        4          4     4            4   4                                           ______________________________________                                    

Such a brushing/shaving treatment which is costly on an industrialscale, becomes superfluous.

We claim:
 1. A process for producing a silicon containing polyethyleneterephthalate comprising forming a prepolymer by direct esterificationbetween ethylene glycol and terephthalic acid to produce a prepolymerhaving a weight average molecular mass Mw between 9,000 and 16,000 and apolydispersity index between 1.5 and 2, continuously introducing methoyethyl or propyl silicate into the prepolymer at a temperature between260° and 290° C. and at a pressure between 1.5 and 2.5 bars,subsequently reacting the silicate/prepolymer mixture and polycondensingthe prepolymer to produce polyethylene terephthalate wherein thesilicate/prepolymer mixture reaction time is at least 5 minutes.
 2. Theprocess according to claim 1, wherein the methoxyethyl or propylsilicate is introduced in a proportion of 400 to 600 ppm of silicon. 3.The process according to claim 1, wherein the prepolymer has aweight-average molecular mass Mw of between 11,000 and 14,000.
 4. Theprocess according to claim 1, wherein the methoxyethyl or propylsilicate is introduced at a time when the prepolymer has apolydispersity index of between 1.7 and 1.9.
 5. The process according toclaim 1, wherein the silicate is introduced at a temperature between275° and 285° C.
 6. The process according to claim 1, characterised inthat the silicate is introduced at a time when the pressure is between1.7 and 2.2 bars.